Displaying page last modified date gives a few advantages to a website. First, and most important to this website, it shows when content is updated. I am poking away at the pages I originally planned to write and I felt like people would have no idea when to read through a page again. More important for most websites, it updates the meta data for the web page. When Google’s site indexer looks at your website, it will rank your website on how current your data is, not when you created the webpage. So, without further ado…
How I added the page last modified date:
Actually this turned out to be easy using the Last Modified Timestamp plugin. Install and activate the plugin from your wordpress dashboard. Then, place the shortcode where you would like the last modified date to appear on your website. For me, the sidebar widget worked great. From your wordpress dashboard click on Appearance > Widgets.

Choose a text widget from the available widgets, select the location (sidebar), and click add widget. Title it as you see fit, I used “Page Updated”.

Add the shortcode to the textbox. Save it and you should be good to go! You can re-order the sidebar simply by dragging and dropping each widget.
When it comes to providing the last modified date to search engines, I have tried yet. The wordpress Last Modified Timestamp plugin page has a description of how to achieve this in the FAQ. I will update this page when I complete the process.
